Ocean carbon sequestration during glacial climates due to combined Antarctic sea ice expansion and ocean circulation change

Abstract: Glacial-interglacial transitions punctuate Earth’s Quaternary climate, accompanied by substantial atmospheric carbon dioxide and ocean carbon storage changes. The cause of atmospheric carbon drawdown during glaciations is uncertain, involving many mechanisms whose interactions are poorly understood. 

Here, we show that the combined expansion of Antarctic sea ice and associated changes in the meridional overturning efficiently sequester carbon in the ocean abyss, leading to a decline in atmospheric carbon dioxide. In contrast, changes in sea ice and circulation individually result in ocean carbon dioxide outgassing. When sea ice expansion and circulation changes act together, they enhance biological carbon storage by reducing ocean-atmosphere fluxes in the Southern Ocean, without invoking external drivers of the biological pump. This reduction inhibits the outgassing of upwelled remineralized carbon and promotes its resubduction into the abyss. 

Together, these results reveal a reinforcing feedback linking atmospheric cooling, Antarctic sea ice expansion, and ocean circulation changes to enhanced biological carbon storage and atmospheric carbon dioxide drawdown.